Conclusion
In the present study, the influence of different concentration of exogenous Ca to P. massoniana seedling growth was illustrated. Ca deficiency resulted in significant growth and development inhibition while adequate exogenous Ca promoted seedling growth and development. The underling mechanisms were deciphered at physiological, proteomic and transcriptional level (Figure 7). Exogenous Ca supply laid a foundation for various Ca signal transduction pathways and intracellular Ca homeostasis. Various primary metabolisms and basic biological process including photosynthesis, carbohydrate metabolism/energy production and nitrogen assimilation/protein metabolism were distributed by Ca deficiency. Sufficient exogenous Ca restored and promoted these pathways and processes through regulating the expression of enzymes and/or proteins involved in these pathways and processes. Secondary metabolism was activated as a result of improved primary metabolisms at high Ca level. In addition, Ca deficiency leads to severe oxidative stress and redox dyshomeostasis. Affluent exogenous Ca relieved this stress and recover redox homeostasis. Moreover, cell wall structure formation/strengthening and cell division processes were benefited by exogenous Ca. Our study conferred a full view for the demonstration of the potential mechanisms underlying exogenous Ca affected P. massoniana seedling growth and development, which may serve as a useful reference and guidance for both pinaceae plant scientific research and pinaceae plant forestry industry.